pminded IMEI etc can't be read be applications
True for regular applications, but...
pminded therefore Google Play can't grab them?
On stock Android, Google Play is not just a regular application. It has many invasive privileges that aren't available to other apps. One of those privileges is the ability to read device identifiers.
pminded And therefore this wouldn't be a specific GOS feature?
Sandboxing Google Play (which prevents it from reading device identifiers, among many other things) is arguably one of the most important features of GrapheneOS.